This invention relates to digital video signal reproducing apparatus and, more particularly, to such apparatus which is capable of reproducing digital video signals at a high speed, thereby providing a high speed play mode, from which a natural looking image may be displayed.
Both analog and digital video recorders are known to record a frame of video signals in a plurality of slant tracks on a magnetic tape. For example, in an analog 8 mm video recorder, one video frame is recorded in two tracks. In a digital video recorder of the type known as the D-2 format, one frame of digital video signals is recorded in 12 slant tracks. Still further, a digital video recorder for consumer use has been proposed, wherein one frame of an NTSC video signal is digitized and recorded in 10 tracks and one frame of a PAL video signal is digitized and recorded in 12 tracks.
In analog and digital video playback devices, such as a video recorder exhibiting a reproducing mode, the previously recorded video signals may be reproduced in both a xe2x80x9cnormalxe2x80x9d playback mode and in xe2x80x9cspecialxe2x80x9d playback modes. In the normal mode, the video tape is transported at a playback speed substantially equal to the speed at which it was driven during a recording operation and, as a result, the heads scan traces which substantially coincide with the previously recorded tracks. However, in a special playback mode, such as in a high speed playback mode, the tape is transported at a much higher speed than the speed at which it was driven during a recording operation and, consequently, each head of the video recorder then scans a portion of each of several tracks. Hence, the resultant image which is reproduced from the data recovered from portions of respective tracks appears as a synthesized display which is perceived as an unnatural image which may be difficult to view.
Therefore, it is an object of the present invention to provide digital video signal reproducing apparatus which reproduces at a high speed digital video signals that had previously been recorded on a magnetic tape, resulting in a video display which appears as a natural image.
Another object of this invention is to provide apparatus of the aforenoted type in which the magnetic tape is transported at predetermined high playback speeds directly related to the head structure of the reproducing apparatus, the number of tracks in which a frame of the digital video signal is recorded and the data read-out rate exhibited by the apparatus.
Various other objects, advantages and features of the present invention will become readily apparent from the ensuing detailed description, and the novel features will be particularly pointed out in the appended claims.
As one aspect of the present invention, apparatus is provided for reproducing digital video signals from a magnetic tape wherein a frame of digital video signals had been recorded in 2 m tracks (m is an integer greater than 1). A pair of rotary heads having respectively different azimuth angles scan traces across the magnetic tape, these traces substantially coinciding with the record tracks when the magnetic tape is transported at a playback speed substantially equal to the transport speed used to record the digital video signals. The tape is transported at a playback speed equal to (mxc3x97nxc2x1E) times the recording speed, where n is an integer other than zero, 1=0.5 when the heads are arranged as a double azimuth head assembly and 1=0.25 when the heads are angularly separated by 180xc2x0.
As another aspect of this invention, each frame of digital video signals is recorded as a multiple of blocks of picture elements, the blocks of a frame being recorded in shuffled form with respect to each other. If the heads are arranged as a double azimuth head assembly, 1=0.5 if the data read-out rate of the reproducing apparatus is at least 50% and 1=0.25 if the data read-out rate is less than 50%. Alternatively, if the heads are angularly separated from each other by 180xc2x0, n is an odd integer and 1=0.25 if the data read-out rate is at least 50% and 1=0.125 if the data read-out rate is less than 50%.
As a feature of this invention, n is a positive number when the tape is transported in a forward direction or a fast forward playback mode; and n is a negative number when the tape is transported in the reverse direction or a fast reverse playback mode.
As another feature of this invention, if the digital video signals are derived from NTSC television signals, m=5. If the digital video signals are derived from PAL television signals, m=6.
As yet another feature of this invention, the frame of digital video signals are recorded as orthogonally transformed video signals, such as video signals that had been subjected to discrete cosine transformation, and are encoded in a variable length code, such as a two-dimension Huffman code.
As a result of the present invention, each head picks up digital video data from a portion of each of multiple tracks scanned by that head during the fast playback operation; and when such picked up portions are assembled in a composite form, they emulate the original record tracks having respective portions from different frames contiguous to each other. That is, a portion of a video signal in one track in one frame is linked to (or abuts) an adjacent portion of a video signal in another track in a different frame. As a result of this linked video data, the resultant image displayed therefrom appears as a natural-looking image.